1. Field of the Invention
The invention relates to a process and a device for adjusting clearing limits that seperate defects in yarn which are to be cut out from defects which are not to be cut out.
2. Background Information
In devices of this type, which are also called yarn clearers, it is conventional to manually adjust a clearing limit in that adjustment values are input in a control apparatus to establish a clearing curve.
This process is very complicated, because good clearing limits can only be found by complicated trials. This means that, with a first clearing limit, yarn is produced and the quality of the yarn and the products produced therefrom is then tested, whence data for the adjustment of a new improved clearing limit has to be found. The clearing limit which has been found must then also finally be adjusted in a plurality of control apparatuses on spinning frames.
A process and a device of the above-mentioned type are known from EP 0 877 108 in which the clearing limit is adjusted automatically. To this end, yarn defects are detected from a first yarn portion, in that values for the thickness and length of thickness variations of the yarn are measured and collected. With the aid of a computer, for example a so-called PC which contains a suitable program, these values can be sorted and displayed in a graph, the values for the thickness and the associated values for the length of the defects being entered in a length/thickness graph. In this graph value ranges for various lengths of defects in the yarn are plotted along one axis and value ranges for the thickness of the defect in the yarn along another axis. Rectangular fields are thus produced which are limited by respective upper and lower limits for the length and upper and lower limits for the thickness of the defect. Defects detected in the yarn can now be entered in the fields in this graph, so for each thickness and length range the number of detected defects is determined and the defect density in this range is obtained.
Since with accurate measurements on the yarn even small deviations in the thickness from an average or from a predetermined value are detected, very many values and therefore also a very large defect density are obtained for these small deviations. These values can be allocated to a so-called “yarn package”. They do not belong to real defects, as in practice they merely reflect the normal structure of the yarn. Only deviations in the thickness which exceed a specific measure are noteworthy. In a first approximation, therefore, the defect density can be ascertained as a measure of the size or significance of the defect, namely as follows: The higher the defect density, the less disruptive is the corresponding defect. An optimum clearing limit should accordingly combine points with identical defect density or identical defect size in one defect graph. Defects which lie on this clearing limit are thus respectively equally disruptive. In this process, the operator inputs the number of clearer cuts into the PC and thus obtains the optimum clearing limit. If the operator agrees with the curve obtained, he loads this into the memory of a control apparatus for the yarn cleaner which continues to work therewith.
A disadvantage of this known process is that the clearing limit is determined on the basis of values for an admissible number of cuts to the yarn. Therefore, the quality of the yarn and the subsequent products possibly needs to be checked and the clearing limit then adapted again.